The Strategic Tunnel Enhancement Programme

The Strategic Tunnel Enhancement Programme (STEP) is a large wastewater construction project that is symptomatic of Abu Dhabi’s growth. As the deep gravity tunnel nears its completion, the city’s surrounding emirates are ready to be inspired.

The Abu Dhabi Sewerage Services Company (ADSSC) is currently managing the STEP project by constructing a huge gravity-driven hydraulic wastewater network.

It will accommodate the projected demands in the emirate for flow and distribution management, involving the island, the mainland, and some neighbouring islands. Once the build is complete, the network will improve the capacity of Abu Dhabi’s waste water system. The station is expected to be fully operational by the last quarter of 2017.

Managing Director of ADSSC, Alan Thomson said, “this centralized system with a deep sewer gravity tunnel was first used in Singapore”. His company has “adopted a similar approach but with changes to match the needs of Abu Dhabi and the UAE as a whole”. This involves “introducing the newest technologies available in the industry”.

The impressive structure consists of three main components: a 41-kilometre tunnel known as the “spine”, 43 kilometres of links, or “ribs”, and a maximum capacity pumping station. The tunnel will start at a depth of 27m underground and will reach a depth of 100m.

The flows will be channelled by gravitational energy down the link sewers, which will relieve the current collector system. The waste will journey to treatment plants and to the pumping station at Al Wathba. This sizeable pumping station has a pumping capacity of 30m3 per second, and is powerful enough to render the 35 existing pumping stations obsolete. The existing stations are, in some cases, 30 years old. In their current state, they are nearing full capacity and would require extensive maintenance without the intervention of this project.

The new station “pushes pumping standards to the limit in terms of size and volumes”, according to the Managing Director. In celebration of the project, he said:

“STEP will have a huge impact in terms of reducing the carbon footprint with our calculations showing that the new pumping station will be much more efficient than the 35 pumping stations it replaces.”

“Only around half a dozen manufacturers in the world can make the pumps we have brought in for this project. On top of that, the state of the art control systems will ensure effective pump management and maintenance. The power to run the pumps requires us to have our own sub-station, along with our own large standby generators in case we have a failure in the electricity grid system”

“We also work with other partners such as Masdar to develop new technologies, reduce energy costs, and utilize any waste products that come out of the process.”

“Our intention is definitely to achieve as close to 100% recycled water use as technically possible throughout the Emirate of Abu Dhabi. We know the demand is there and we will have 100% recycled water to all intents and purposes by the time the deadline was set.”

Mott MacDonald is providing site overview and administrative services for the project. Mr. Peter Hall, Mott MacDonald’s project director, said: “The UAE is the third largest consumer of water in the world after Canada and the USA. There is a daily water consumption rate of nearly 550 litres per person in a region that receives less than 1cm of rain per year. Therefore, management and reuse of wastewater is a critical component to Abu Dhabi’s long-term sustainability.”

Alan Thomson also commented on mass consumption. He said:

“Most people do not think too hard about the utilities they use, including water.”

Most of the wastewater is of domestic origin, as opposed to industrial. Nevertheless, there has been an increase in this type of waste over the past three decades.

“Currently, we see a doubling of volumes [of water in Abu Dhabi] every 10 years, starting in 1982. At some point that will surely level out; however, for the near to medium future, we expect that rate of increase to continue. Concerns only arise whenever there is a problem in receiving the service. We still have an important role to play in conveying to people that water is a limited resource and that its usage has a huge impact on the environment. One of the ways to do this is to make water valuable to consumers by charging a realistic price for it. A cost reflective charge makes people more careful about how they can stop wasting resources like water and power.”

In light of this, the ADSSC plans to educate citizens in the public domain, visiting schools, businesses and hospitals to send the message: “If you didn’t have water and sanitation, everyone’s health would suffer. Therefore, it is an important service, and one that people should not take for granted. People should recognize that it is expensive to run a sewage or water business, especially in the desert.” Spreading this message should help people to understand that water should be valued and respected instead of overused and wasted. Despite this, the ADSSC will utilize the STEP program and “look at the continued growth of Abu Dhabi and what its future needs are in terms of meeting customer requirements.”

The project has had positive influence on the job market in Abu Dhabi. It has engaged with 20,000 employees, across a dimension of roles, with project managers, contractors, excavators and engineers working together for completion in 2018. By working closely with the private sector, STEP has recruited its employees from a solid private sector of people trained to the highest of standards. This system helps to retain the staff as well, as their high quality work continues to impress their employers. Alan Thomson said, “We are looking for partnerships where we are all working together as opposed to against each other. We obviously entered into contracts with consultants and contractors to deliver services. We expect high-quality service, but we also look for long-term relationships where we work in harmony with these contractors and consultants. As time goes on, they understand our business better so they can produce a better service for us.”

Due to the enormous scale of the build, the construction has been split in to separate sections. The sections of the main tunnel are named T-01, T-02 and T-03. A link station called LS-01 has been built at Abu Dhabi Island, and a second station (LS-02) has been built in Abu Dhabi main land, which together comprise of the link sewers, and a pump station.

Multiple contracts have been awarded to manage the sections. Samsung C&T Corporation of South Korea is carrying out the tunnelling of section T-01 of the main tunnel. Three tunnel boring machines (TBMs) supplied by Kawasaki Heavy Industries are being used for the construction.

Impregilo Group was awarded the contract to construct the T-02 stretching 15km in September 2009. The tunnelling was done with an excavated diameter of 6.3m, which includes six access shafts at depths of 40m to 50m.

Impregilo Group was further awarded a contract to construct T-03 stretching 10.5km in November 2010. The work involved excavation at a diameter of seven metres and construction of four access shafts at depths of 60m to 80m.

The contract for the construction of link sewer LS-01 and LS-02 has been awarded to Zublin. The sewers are being constructed using a pipe jacking method. Hydraulic jacks are used to push pipes through the ground behind a shield whilst the excavation takes place within the shield. The construction of LS-01 necessitates excavation at diameters ranging from 200mm to 2,800mm, and requires the construction of about 247 shafts. The construction of LS-02 needs excavation works at diameters ranging from 200mm to 3,100mm and will require 95 shafts.

The contract for the construction of the pumping station has been awarded to Odebretch, while Drake & Scull Water and Power (DSWP) will carry out the design review, procurement and construction of mechanical, electrical and plumbing (MEP) and instrumentation works for the facility.

Unibeton Ready Mix has been awarded the contract to supply the concretes for the link tunnels. The company was also involved in supplying the ready mix concrete for T-02 and T-03 parts of the main tunnel. GE will supply eight pump drive trains, including pump process automation for the pumping station. The pump drive trains will be rated at 6.38MW each.

Commodore Cement Industries has so far supplied more than 17,700 lining segments for the project. The company will also supply more than 40km of jacking pipes with internal diameters ranging from 700mm to 3,100mm, including several access shaft segments for the link sewers. The hydraulic tunnel and the access shafts are being lined with a special membrane to protect the concrete sections.

The tunnel is designed to last for about 100 years: a long-term investment to Abu Dhabi.

The overall cost of the project is $1.9 billion, which currently equates to 6.98Dh.

It is set to triple Abu Dhabi’s sewage network capacity, and will accommodate for an average wastewater flow of 800,000 m3/day, which is set to reach an ultimate capacity of 1.7 million m3/day by the year 2030.

Mr. Thomson has highlighted the progress of the project, saying “STEP has been a feature of ADSSC since we started in work on it in 2008. Construction work started with our first tunnel contract in 2009. At the moment we are at the tail-end phase of its construction, which ran a little longer than anticipated due to construction issues at the pumping station.”

In spite of these setbacks, the Managing Director explains that it takes “several years” to build sewage infrastructure, especially when it is required on such a great scale. He notes the importance of planning “well in advance, because as more people come into the area, you have to think about how you plan downstream. New development impacts on the downstream development, meaning you have to allow for downstream flows when you examine upstream development.”

Now that the pumping station is substantially complete, Mr. Thomson has confirmed that the ADSSC have “successfully introduced sewage on a small scale to test some of the pumps and technology.” The testing is designed to be as non-invasive as possible, and “locations are chosen because they have specifically low impact on the public. They tend to be off the street… they tend to be perhaps in a central reservation where they are not obstructing any traffic flow.”

Disturbances are also minimized because all of the work is cultivated underground.

STEP has been enlisted as part of the company’s strategy for the ‘5 years plan’, which incorporates the General Policy Agenda of Abu Dhabi municipality in accordance with a strategic plan of 2030 projecting his R.H Sheikh Khalifa Ben Zayed Al Nahyan, vision, which engulfs the continuity of secure social and economic development open to international compatibility

A considerable component of the plan is to depressurize the system and relieve the stress that is currently being put on the waste network. The program offers a unique solution to copious wastage that will carry an effective and qualitative value in terms of cost and sustainability; once treated, the wastewater will return to the metropolitan areas for irrigation purposes. This will help to meet the long-term island demands.

The encouraging level of growth and development in Abu Dhabi has helped to inspire a wider ranging national agenda known as the UAE Vision 2021. This bold vision aims to make the United Arab Emirates one of the world leaders on quality infrastructure, in time for the golden jubilee celebrations.

On reflection, it is clear that the ADSSC have “made a great start, but…can make further improvements with continued cooperation”. With this optimistic sentiment in mind, it is reasonable to say that Abu Dhabi is building its reputation as a leader in infrastructure, and it is very likely that the STEP will cement this reputation.